$$\mathbf {L^p\rightarrow L^q}$$ bounds for spherical maximal operators

Abstract

Let \(f\in L^p({\mathbb {R}}^d)\), \(d\ge 3\), and let \(A_t f(x)\) be the average of f over the sphere with radius t centered at x. For a subset E of [1, 2] we prove close to sharp \(L^p\rightarrow L^q\) estimates for the maximal function \(\sup _{t\in E} |A_t f|\). A new feature is the dependence of the results on both the upper Minkowski dimension of E and the Assouad dimension of E. The result can be applied to prove sparse domination bounds for a related global spherical maximal function.